Solvent‐Free Synthesis of Closed‐Loop Recyclable Acetal Thermosets Derived from Biobased Resources

Thermosetting plastics are essential in industry and daily life due to their superior thermal and mechanical properties, however their nonrecyclability and reliance on petroleum resources pose environmental concerns. Developing biobased thermosets with efficient chemical recycling capabilities is therefore crucial for advancing a circular plastic economy and reducing environmental impact. Herein, this study reports the synthesis of recyclable acetal thermosets via the polycondensation of a biobased vanillin-derived aldehyde and diols, utilizing oxalic acid as a catalyst, which can be easily removed during thermal postcuring. The resulting thermosets exhibit excellent mechanical performance, with tensile strengths up to 95 MPa, Young's moduli of ≈3.3 GPa, and a glass transition temperature (T_g) of ≈70 °C. More importantly, the thermosets are efficiently depolymerized under mild acidic conditions into their original monomers, which are easily isolated in high purity, with yields of 72% and 98% for the diol and aldehyde, respectively. These monomers were subsequently reused to synthesize new, identical thermosets, achieving closed-loop recycling. This research addresses the environmental challenges posed by traditional thermosets, offering a practical solution for sustainable polymer recycling without compromising material performance. The solvent-free approach further enhances its industrial viability, making a promising step toward a more sustainable strategy for closed-loop recyclable thermosets.